(57) A kind of gear is provided with shorter teeth, transition teeth and at least one
longer tooth. The cross-section of the longer tooth is of a hawk beak shape, and the
profile of the longer tooth is smoothly connected in series by a convex section, a
tip section, a concave section, and a leading section. The two sides of the longer
tooth are each provided with a transition tooth which neighbors a shorter tooth on
the opposite side of the longer tooth. The pair of engaging gears according to this
invention has advantages of reducing the fluid leakage, canceling the inertia of the
rotors, and minimizing the vibration and noise. This invention also discloses a fluid
machine for conveying, compressing or expanding liquid or gaseous fluids, which includes
a casing comprising a housing, an upper end cover and a lower end cover. At least
one pair of engaging gears which includes one driving rotor according to this invention
and one driven rotor according to this invention is accommodated in the housing. As
a result, the leakage between the rotors can be reduced, therefore the compression
ratio can be improved. In addition, over compression and under compression can be
avoided in operation.
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